In a lithography process for manufacturing a semiconductor element, liquid crystal display element, or the like, an exposure apparatus has been used which transfers a pattern formed on a mask or reticle (to be generically referred to as a “reticle” hereinafter) onto a substrate such as a wafer or glass plate (to be referred to as a “wafer” hereinafter) through a projection optical system. As such an exposure apparatus, a stationary-exposure-type projection exposure apparatus such as the so-called stepper, or a scanning-exposure-type projection exposure apparatus such as the so-called scanning stepper is mainly used.
In such an exposure apparatus, it is necessary to perform highly accurate alignment between the reticle and wafer before exposure. To perform this alignment, because a position detection mark (alignment mark) that is formed (transferred) in the previous photolithography process is provide on each shot area on the wafer, by detecting this alignment mark, the position of the wafer (or a circuit pattern on the wafer) can be detected. And on the basis of the detection result of the position of the wafer (or a circuit pattern on the wafer), the alignment is performed.
Therefore, the accuracy of alignment is determined by the accuracy of detecting the position of the alignment mark. Accordingly, to perform the alignment with high accuracy, it is necessary to detect the position of the alignment mark with high accuracy.
Several methods of detecting the position of an alignment mark on a wafer are actually used. However, in any method, by analyzing the waveform of a detected signal of the alignment mark that is obtained by a detector for position detection, the position of the alignment mark on the wafer is detected. For example, in position detection through use of image detection that is popularly used these days, the position of the alignment mark is detected by picking up an optical image of the alignment mark through use of a picking-up unit and analyzing the light intensity distribution of its picked-up signal, i.e. the image.
As such a method of analyzing a signal waveform, a pattern matching (template matching) method which examines correlation between the signal waveform and a template waveform, which is prepared beforehand, by using as a parameter the position of the alignment mark that is detected by picking-up is attracting a lot of attention. By analyzing a signal waveform through use of this pattern matching method and obtaining a value of the parameter at which the correlation between the signal waveform and the template waveform is highest, the position of the alignment mark is detected.
As a template used for the above pattern matching, a theoretical signal waveform obtained from the design shape of the alignment mark, or a waveform composed of average values obtained by calculating the average of measured waveforms of a predetermined number of alignment marks has been used.
When using the above theoretical signal waveform as the template waveform, depending on difference between the design shape of the alignment mark and its actual shape, non-negligible error may occur in the detection result of the position of the alignment mark. As opposed to this, such an error can be avoided by using the above average-value-waveform as the template waveform.
Although the average-value-waveform has been obtained by calculating the average of the respective values (e.g., voltage values reflecting light intensity), at each position on a coordinate, of a plurality of measured signal waveforms, in actually measured signal waveforms, there are positions where the signal level of any of the signal waveforms is near the average and other positions where their signal levels are somewhat different. Therefore, when the differences of the signal levels in some positions are very large, accurate position may be detected by performing pattern matching while taking into account positions except for those positions rather than taking all positions into account, even though the amount of processing decreases.
Because the number of signal waveforms that are measured beforehand to generate the average-value-waveform as the template waveform is finite, the accuracy of matching with a newly measured signal waveform having a shape that is not reflected by the template waveform is always low. Especially, when a newly measured signal waveform can not be expressed as interpolation of signal waveforms used for generation of the template waveform, the matching accuracy decreases. To avoid such a situation, it is necessary to measure a huge amount of signal waveforms beforehand and generate a template waveform covering all possible signal waveforms, and therefore it takes a lot of time to generate the template in order to prepare for the template matching.
The present invention is invented under such a circumstance. A first purpose of the present invention is to provide a pattern matching method and pattern matching unit that can easily generate a template and perform template matching with improved accuracy.
In addition, a second purpose of the present invention is to provide a position detection method and positional detector that can accurately detect the positions of measured marks.
In addition, a third purpose of the present invention is to provide a alignment method and alignment unit that can accurately align a body on which the marks are formed.
Furthermore, a fourth purpose of the present invention is to provide an exposure method and exposure apparatus that can accurately transfer a predetermined pattern onto a substrate.
Additionally, a fifth purpose of the present invention is to provide a device on which a fine pattern is accurately formed and its manufacturing method.